YC S21 Batch — Companies, Valuations, and What Happened Next

S21 is consequently both the most exciting batch to study and the most cautionary. The ease of capital in 2021 funded some exceptional companies — but it also funded many companies that would not have raised in a normal market, and the valuations set in September 2021 created down-round pressure for companies that grew into the correction.

• Batch size: ~377 companies (all-time record at the time)
• Demo day: September 2021
• Fundraising environment: Peak — easiest fundraising in YC history
• Median seed round: ~$4-5M (all-time high)
• AI proportion: ~18%
• International proportion: ~42%
• Defining risk: Inflated valuations creating down-round pressure in 2022-2023

Software and Developer Tools

Notable S21 Developer Tools companies:

B2B SaaS

Notable S21 B2B SaaS companies:

Fintech

Notable S21 Fintech companies:

Healthcare

Notable S21 Healthcare companies:

AI and Machine Learning

Notable S21 AI companies:

Indian-Origin S21 Companies

Peak 2021 Valuations

S21 demo day in September 2021 produced the highest valuations in YC batch history. Several notable data points:

S21 seed round statistics:

• Median seed round: $4.5M (vs $2.1M for S22 post-correction)
• Average valuation cap: $20M (vs $10-12M post-correction)
• Fastest seed closes: Multiple companies closed $5M+ rounds within 72 hours of demo day
• Largest S21 seed round: $20M+ for top-tier companies

The valuation problem that emerged in 2022-2023:

Companies that raised at $20-30M caps in September 2021 needed to grow revenue significantly before their next round — otherwise they faced flat or down rounds. The correction meant that companies raising Series A in 2022-2023 often found that their 2021 seed valuation was close to or above what Series A investors would pay at Series A metrics.

S21 Companies That Navigated the Valuation Trap

The S21 companies that successfully raised Series A in 2022-2024 without down rounds share a common pattern: they grew revenue 3-5x between seed and Series A, maintained strong retention, and raised when they could demonstrate Series A-quality metrics rather than raising on timeline.

Notable S21 Series A raises:

• WorkOS: $80M at strong valuation — enterprise readiness product with real enterprise revenue
• Orb: $50M Series B — usage-based billing with $10M+ ARR
• Parafin: $100M — marketplace capital with strong default rates
• Mercury: $300M+ — banking product with 100,000+ customers
• Medallion: $85M — healthcare credentialing with major health system clients

S21 Companies That Struggled

Not every S21 company benefited from the peak funding environment. Several categories experienced high failure rates:

• Consumer fintech: Several S21 consumer fintech companies raised at peak valuations on growth metrics that proved unsustainable when the consumer spending boom of 2021 normalized.
• NFT and crypto: S21 had a significant crypto cohort that was decimated by the 2022 crypto winter.
• Consumer social: Several S21 social apps raised at high valuations on early engagement metrics that did not translate to durable retention.

S21 is a complete case study in how funding environment shapes startup outcomes — both positively and negatively.

The positive S21 legacy:

Several of today's most significant fintech and infrastructure companies trace their origin to the S21 batch. Ramp, Mercury, WorkOS, and Medallion are building category-defining businesses. The extended runway from their 2021 fundraises gave them time to build product depth and customer bases that survived the correction.

The negative S21 legacy:

The S21 batch also includes some of the clearest examples of what happens when capital is too easy — companies that raised on narrative without product-market fit, inflated valuations that created unrealistic growth requirements, and a cohort psychology where "raise as much as possible" replaced "build sustainably."

What S21 teaches founders today:

1. Take the money when the market is open, but deploy it like it might be the last you raise. S21 companies that deployed their peak-valuation capital efficiently — into product, into hiring that created compounding returns — are the ones thriving in 2025. Companies that deployed it into office space, large teams, and marketing spend are largely gone.
2. Valuation caps are obligations, not compliments. A $25M seed valuation requires you to be worth significantly more at Series A. Know what revenue and retention metrics justify your next round before you set the valuation on your current one.
3. The best S21 companies ignored the market euphoria. The founders of Ramp, Mercury, and WorkOS built the same way they would have in any market — focused on revenue, focused on retention, focused on product quality. The market gave them extra capital; they used it to go faster, not to go differently.